1. Field of the Invention
The present invention relates generally to the field of oligonucleotide chemistry and anti-viral pharmacotherapy. More specifically, the present invention relates to novel guanosine-rich oligonucleotides and their use as novel anti-viral agents.
2. Description of the Related Art
Previously, it was believed that "antisense" oligonucleotides inhibit viruses by interfering with protein translation via an RNA:DNA duplex structure. More recent research, however, indicates a variety of possible mechanisms by which oligonucleotides inhibit viral infections. For example, oligodeoxycytidine (poly SdC) inhibits HIV-1. Marshall et al., PNAS (1992) 89:6265-6269, discussed the potential mechanism (competitive inhibition) by which oligodeoxycytidine directly inhibits viral reverse transcriptase. Poly SdC also inhibited AMV reverse transcriptase and Pol I (Klenow fragment) and polymerase .alpha., .beta. and .gamma.. Previously, Matsukura et al., PNAS (1987) 84:7706-7710, used a similar phosphorothioate derivative of oligodeoxycytidine to demonstrate inhibition of HIV-1 in culture. Marshall and Caruthers, Science (1993) 259:1564-1569, reported the use of diphosphorothioate oligonucleotides, e.g., antisense specific, random nucleotide combinations and oligodeoxycytidine against HIV-1. In all cases, the mechanism of action was attributed to a direct inhibition of HIV-1 reverse transcriptase. Other potential mechanisms of anti-viral action of oligonucleotides were postulated by Boiziau et al., PNAS (1992) 89:768-772, e.g., promotion of RNAse H activity and inhibition of reverse transcriptase initiating cDNA synthesis. In addition, Goa et al., Molecular Pharmacology (1992) 41:223-229 reported that phosphorothioate oligonucleotides inhibit human DNA polymerases and RNAse H, and the adsorption or penetration of the virus into cells. Iyer et al., Nucleic Acids Research (1990) 18:2855-2859 report that if a base was removed from an anti-sense polynucleotide forming an abasic site, the compound did not lose its activity which argues against the need for the formation of an RNA:DNA antisense mediated hybrid for anti-viral activity. Stein et al. have characterized the interaction of poly SdC with the V3 loop of HIV-1 gp120, and postulated that the specific interaction of poly SdC with the HIV-1 V3 loop may be a mechanism by which an oligonucleotide could inhibit HIV-1 in vivo.
It is known that synthetic oligonucleotides may be designed which are capable of binding to duplex DNA to form triplex DNA. See U.S. Pat. No. 5,176,996 Hogan & Kessler issued Jan. 5, 1993. This application describes a method for making synthetic guanosine-rich oligonucleotides which are targeted to specific sequences in duplex DNA and which form colinear triplexes by binding to the major groove of the DNA duplex.